Glass composition for bonding a phosphor and a fluorescent lamp

ABSTRACT

The object of the present invention is to provide a glass composition which has a sufficient bonding strength for bonding a fluorescent film with a glass tube, does not hinder decomposition of the binder and is effective as an adhesive material, and to provide a fluorescent lamp using the glass composition. The object can be achieved by a glass composition, represented by the general formula, 
     
         xMO.yB.sub.2 O.sub.3.zM&#39;.sub.2 O.sub.3.uM&#34;O.sub.2.vM&#39;&#34;.sub.2 O.sub.5 
    
     in which M is at least one element of Mg, Ca, Sr, Ba and Zn, M&#39; is at least one element of Al, Sc, Y and lanthanoid elements, M&#34; is at least one element of Ti, Zr, Hf, Th and Si, M&#39;&#34; is at least one element of Nb and Ta, x, y, z, u and v satisfy the relationships of 0&lt;x≦70, 15≦y≦80, 0≦z≦50, 0≦u≦30, 0≦v≦30, 0.5≦u+v≦50 and x+y+z+u+v=100, represented by mol %, and by a fluorescent lamp, in which the glass composition is incorporated in a phosphor layer in a proportion of 0.1 to 10 weight %.

TECHNICAL FIELD

This invention relates to a low melting point, less water-soluble glasscomposition for bonding a phosphor, which is suitable for bonding afluorescent film to a glass tube in the production of a fluorescentlamp, and to a fluorescent lamp using the same.

BACKGROUND TECHNIQUE

Up to the present time, production of a fluorescent lamp has generallybeen carried out by dissolving nitrocellulose as a binder in an organicsolvent such as butyl acetate, etc. to prepare a solution, in which aphosphor is then suspended, adding an adhesive material consisting of adivalent metal borate having a composition of BaO.CaO.B₂ O₃ for thepurpose of tenacious adhesion of the fluorescent film to the innersurface of a glass tube to the suspension, followed by adequatelymixing, coating the resulting phosphor-coating liquid onto the innersurface of the glass tube, drying, baking to decompose and remove thebinder and thus forming the fluorescent film.

Herein, the method of using such an organic coating composition hasvarious problems of difficulty in handling, safety, poisonous character,economy, etc. and lately, has gradually been replaced by a method ofusing an aqueous phosphor-coating liquid. When using the above describedadhesive material for the organic coating composition, i.e. BaO.CaO.B₂O₃ in an aqueous phosphor-coating liquid, however, there arises aproblem that BaO.CaO.B₂ O₃ tends to be dissolved in water as a solventand its precipitate hinders the decomposition of the binder duringbaking, thus retaining carbon in the fluorescent film.

Thus, there have been proposed methods of using, as an adhesive materialfor an aqueous phosphor-coating liquid, aluminum oxide (Japanese PatentPublication No. 28668/1965), calcium pyrophosphate (Japanese PatentPublication No. 7440/1970), a low melting point glass (Japanese PatentPublication No. 1778/1991), etc.

When using aluminum oxide or calcium pyrophosphate as an adhesivematerial, however, there arises a problem that since a fluorescent filmand a glass tube are bonded through van der Waals force, the bondingstrength is weak and in particular, a circular fluorescent lamp obtainedby bending the tube after forming the fluorescent film tends to oftenmeet with peeling of the fluorescent film. In the case of using a lowmelting point glass as an adhesive material on the other hand, afluorescent film is bonded to a glass tube by fusion and the bondingstrength is sufficient, but the water resisting property is inferior.

Thus, it has been proposed to render a low melting point glass as anadhesive material less water-soluble by adding at least one of Al₂ O₃,SiO₂ and Sb₂ O₃ and an oxide of at least one of Y and lanthanoids (Ln)to a borate of at least one divalent metal selected from Mg, Ca, Sr, Baand Zn (Japanese Patent Publication No. 1778/1991).

In this method, however, there arises a problem that the water resistingproperty is not sufficient and when the adhesive material is crushed infine grains and suspended in water, the fine grains are dissolved inwater. Accordingly, it has eagerly been desired to develop an adhesivematerial such that when a phosphor-coating liquid is coated onto a glasstube, the bonding strength of the fluorescent film with the glass tubeis sufficently large and decomposition of the binder is not hindered.

The present invention aims at providing a glass composition for bondinga phosphor (which will hereinafter be referred to as "glasscomposition"), which has a sufficient bonding strength for bonding thefluorescent film with the glass tube, does not hinder decomposition ofthe binder and is effective as an adhesive material, and to afluorescent lamp using the glass composition.

DISCLOSURE OF THE INVENTION

The above described problems can be solved by employing the followingconstruction elements according to the present invention:

(1) A glass composition represented by the general formula,

    xMO.yB.sub.2 O.sub.3.zM'.sub.2 O.sub.3.uM"O.sub.2.vM'".sub.2 O.sub.5

in which M is at least one element of Mg, Ca, Sr, Ba and Zn, M' is atleast one element of Al, Sc, Y and lanthanoid elements, M" is at leastone element of Ti, Zr, Hf, Th and Si, M'" is at least one element of Nband Ta, x, y, z, u and v satisfy the relationships of 0<x≦70, 15≦y≦80,0≦z≦50, 0≦u≦30, 0≦v≦30, 0.5≦u+v≦50 and x+y+z+u+v=100, represented by mol%.

(2) The glass composition as described in above (1), wherein x, y, z, uand v satisfy the relationships of 5≦x≦65, 30≦y≦70, 0≦z≦40, 0≦u≦30,0≦v≦20 and 1≦u+v≦40.

(3) A glass composition represented by the general formula,

    xZnO.yB.sub.2 O.sub.3.zM'.sub.2 O.sub.3.uM"O.sub.2.vM'".sub.2 O.sub.5

in which M' is at least one element of Al and Sc, M" is at least oneelement of Ti, Zr, Hf, Th and Si, M'" is at least one element of Nb andTa, x, y, z, u and v satisfy the relationships of 5≦x≦70, 25≦y≦75,0≦z≦40, 0≦u≦30, 0≦v≦30 and x+y+z+u+v=100.

(4) The glass composition as described in above (3), wherein x, y, z, uand v satisfy the relationships of 10≦x≦65, 30≦y≦65, 0≦z≦35, 0≦u≦25 and0≦v≦20.

(5) The glass composition as described in any one of above (1) to (4),wherein the softening point is in a temperature range of 600° to 700° C.

(6) The glass composition for bonding a phosphor as described in any oneof above (1) to (5), wherein the water solubility is at most 200 μS/cmrepresented by electric conductivity.

(7) A fluorescent lamp, in which the glass composition described in anyone of above (1) to (6) is incorporated in a phosphor layer on the innersurface of a glass tube in a proportion of 0.1 to 10 weight %.

By employing these constructions, there can be provided a low meltingpoint glass having a good softening point and water resisting propertyas well as being excellent as an adhesive material of a phosphor, and afluorescent lamp having a good fluorescent film without retainingcarbon.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 shows a DTA curve of a glass composition obtained in Example 1 ofthe present invention.

BEST EMBODIMENT FOR CARRYING OUT THE INVENTION

The functions of the present invention will be illustrated by apreferred embodiment thereof.

Generally, the glass composition used as an adhesive material forforming a fluorescent film of a fluorescent lamp should be softened at atemperature range of 600° to 700° (as a first condition) between thebaking temperature (500° to 600° C.) in the production of thefluorescent lamp and the cicuular fluorescent lamp bending temperature(700° to 800° C.), because if baking is conducted at 500° to 600° C. soas to remove the binder in the fluorescent film after coating thephosphor-coating liquid onto an inner wall of a glass tube, the glasscomposition as the adhesive material is softened and the binder in thefluorescent film is caught up, thus blackening the fluorescent film. Inorder to avoid this, it is necessary to adjust the softening point ofthe glass composition to higher than the baking temperature.

In the production of a circular fluorescent lamp, the tube bendingoperation is carried out at 700° to 800° C. If the glass composition isnot softened at this operation temperature, the phosphor is not capableof maintaining the bonding with the glass tube and is thus peeled.Namely, the glass composition does not function as an adhesive material.Accordingly, it is necessary to adjust the softening point of the glasscomposition to lower than the tube bending operation temperature.

Furthermore, it is required that the glass composition used as anadhesive material is insoluble in solvents (the solvent being water inthe case of aqueous phosphor-coating liquid) (as a second condition).The reason therefor is that if the glass composition is dissoved inwater, the once dissolved material is again precipitated during dryingthe fluorescent film and surrounds an organic binder, so thatdecomposition of the organic binder is hindered during baking to retaincarbon.

Thus, the inventors have prepared by way of trial a number of glasscompositions while changing combinations of various metal oxides asglass constituting components and compounding ratios thereof, followedby subjecting them to analysis, and consequently, have found a lowmelting point glass composition having a good softening point and waterresisting property as well as characteristics suitable for use as anadhesive material of a fluorescent film for a fluorescent lamp.

The glass composition of the present invention has a compositionrepresented by the general formula,

    xMO.yB.sub.2 O.sub.3.zM'.sub.2 O.sub.3.uM"O.sub.2.vM'".sub.2 O.sub.5

in which M is at least one element of Mg, Ca, Sr, Ba and Zn, M' is atleast one element of Al, Sc, Y and lanthanoid elements, M" is at leastone element of Ti, Zr, Hf, Th and Si, M'" is at least one element of Nband Ta, x, y, z, u and v satisfy the relationships of 0<x≦70, 15≦y≦80,0≦z≦50, 0≦u≦30, 0≦v≦30, 0.5≦u+v≦50 and x+y+z+u+v=100, represented by mol%.

In the above described general formula, if the values of x, y, z, u andv are outside the above described range, the water resisting propertyand softening point of the resulting composition cannot maintain thecharacteristics suitable for the fluorescent film of a fluorescent lamp,while if x, y, z, u and v satisfy the above described ranges, the waterresisting property and softening point desirable for an adhesivematerial can be maintained and if x, y, z, u and v satisfy therelationships of 5≦x≦65, 30≦y≦70, 0≦z'40, 0≦u≦30, 0≦v≦20 and 1≦u+v≦40,more preferable properties as an adhesive material can be attained.

The other glass composition of the present invention has a compositionrepresented by the general formula,

    xZnO.yB.sub.2 O.sub.3.zM'.sub.2 O.sub.3.uM"O.sub.2.vM'".sub.2 O.sub.5

in which M' is at least one element of Al and Sc, M" is at least oneelement of Ti, Zr, Hf, Th and Si, M'" is at least one element of Nb andTa, x, y, z, u and v satisfy the relationships of 5≦x≦70, 25≦y≦75,0≦z≦40, 0≦u≦30, 0≦v≦30 and x+y+z+u+v=100.

In the above described general formula, if the values of x, y, z, u andv satisfy the above described ranges, the water resisting property andsoftening point suitable for an adhesive material of a fluorescent filmfor a fluorescent lamp can be maintained and if x, y, z, u and v satisfythe relationships of 10≦x≦65, 30≦y≦65, 0≦z≦35, 0≦u≦25 and 0≦v≦20, morepreferable properties as an adhesive material can be attained.

The glass composition of the present invention preferably has asoftening point in a temperature range of 600° to 700° C. and a watersolubility of at most 200 μS/cm represented by electric conductivity.

The fluorescent lamp of the present invention is obtained by coating aphosphor-coating liquid containing 0.1 to 10 weight %, preferably 0.5 to5.0 weight % of the above described glass composition onto a wall of aglass tube.

In the glass composition of the present invention, the network former(NWF) is B₂ O₃, but when using only this component, the water resistingproperty and softening point are too low to be put to practical use.Accordingly, an oxide of another element is required as the networkmodifier (NWM).

In the glass composition of the present invention, as the networkmodifier, there is used a predetermined quantity of divalent metal oxiderepresentd by MO (M is at least one of Mg, Ca, Sr, Ba and Zn). When thisdivalent metal oxide is added, the glass-forming ability is improved andcrystallization of the glass hardly occurs, but in the case of usinganother divalent metal oxide than that of Zn, the water resistingproperty is low.

Thus, a predetermined quantity of trivalent metal oxide represented byM'₂ O₃ (M' is at least one element of Al, Sc, Y and lanthanoid elements)is further used as an oxide of the other element. The addition of thetrivalent metal oxide represented by M'₂ O₃ results in advantages ofimproving the glass-forming ability as well as largely improving thewater resisting property.

Furthermore, in the glass composition of the present invention, thewater resisting property is more improved by adding a predeterminedquantity of tetra-valent metal oxide represented by M"O₂ (M" is at leastone element of Ti, Zr, Hf, Th and Si) and a predetermined quantity ofpenta-valent metal oxide represented by M'"₂ O₅ (M'"is at least oneelement of Nb and Ta).

When the divalent metal oxide consists of only ZnO, the water resistingproperty is more excellent than when using other divalent metal oxides,but in this case, the water resisting property is also more improved byadding, as the network modifier (NWM), predetermined quantities of theabove described trivalent metal oxide represented by M'₂ O₃,tetra-valent metal oxide represented by M"O₂ and/or penta-valent metaloxide represented by M'"₂ O₅.

Production of the glass composition of the present invention isgenerally carried out by weighing raw materials comprising oxidesrepresented by MO such as ZnO, B₂ O₃, M'₂ O₃, M"O₂ and M'"₂ O₅ orcompounds of M, B, M', M" and M'" capable of being converted into theseoxides at high temperatures, for example, carbonates, oxalates,hydroxides, etc. of these elements in amounts of stoichiometricallyforming xMO.yB₂ O₃.zM'₂ O₃.uM"O₂.vM'"₂ O₅ or XZnO.yB₂ O₃.zM'₂O₃.uM"O₂.vM'"₂ O₅, adequately mixing the raw materials, charging themixture in a heat resistant vessel such as a platinum crucible, heatingand fusing it in a high temperature furnace at a temperature of 1000° to1500° C. for 1 to 2 hours, withdrawing the product out of the furnace,rapidly cooling it, crushing the product by a mortar in fine powder andsieving it in a predetermined grain diameter range to obtain a glasspowder.

In addition, the fluorescent lamp of the present invention can beproduced by dispersing a desired phosphor in an aqueous solution binderof polyethylene oxide, to which a predetermined quantity of the abovedescribed glass composition is added, converting the resulting mixtureinto a slurry to prepare a phosphor-coating liquid, coating this coatingliquid onto a glass tube of the fluorescent lamp and then subjecting toa well known processing.

The quantity of the glass composition of the present invention to beadded to a phosphor-coating liquid is 0.1 to 10 weight %, preferably 0.5to 5.0 weight % based on the phosphor, since if the quanity is less than0.1 weight %, the bonding strength of a fluorescent film is notsufficient, while if more than 10 weight %, the emission luminance ofthe resulting fluorescent lamp is lowered.

Whether the glass composition is good or bad as an adhesive material isjudged by the carbon-retained state in a fluorescent film after a bakingstep, the presence or absence of peeling of the fluorescent film from aglass tube wall during a step of producing a fluorescent lamp and thefinished state of the fluorescent film after coating thephosphor-coating liquid.

The carbon-retained state in a fluorescent film is judged by thewhiteness of the body color of a glass tube after baking the fluorescentfilm formed on the inner wall of the glass tube. The less the retainedquantity of carbon, the more white the body color of the glass tube, onwhich the fluorescent film is formed, and the higher the reflectance ofthe glass tube. A fluorescent lamp using the glass composition of thepresent invention as an adhesive material exhibits a higher reflectance.

When the bonding strength of a fluorescent film is insufficient, peelingof the fluorescent film occurs at the end of the tube in a step ofevacuating the tube after forming the fluorescent film on the inner wallof the glass tube, that is, when the tube is evacuated or whenthereafter, Ar gas is rapidly introduced into the tube.

When a predetermined quantity of the glass composition of the presentinvention is used as an adhesive material, the fluorescent film is notpeeled, nor are abnormal changes found.

EXAMPLE

Measurement of Softening Point

Measurement of the softening point of the glass composition is carriedout by subjecting a sample obtained by crushing in at most 20 μm by amortar and sieving to DTA measurement (differential thermal analysis) ata temperature raising rate of 10° C./min using an alumina sample as areference sample and reading the temperature at Point A in the resultingcurve (Cf. FIG. 1) as a softening point. Thus, such a judgment is madethat a sample having a softening point of 600° to 700° C. is apreferable glass composition as an adhesive material of a fluorescentfilm for a circular fluorescent lamp.

Measurement of Water Solubility

For the measurement of the solubility in water of the glass composition,the glass composition is subjected to an elution treatment according tothe test method of a glass instrument for chemical analysis, stipulatedin JIS R 8502. Firstly, a sample is crushed and sieved in 250 to 420 μm,washed with ethanol to remove a finer powder, dried, after which aspecific gravity gram portion (same gram number as numeral of specificgravity) is weighed, charged in a pot of 250 ml in voloume with 100 g ofdeionized water and subjected to rolling at a revolution number of 100rpm for 20 hours, and the electric conductivity of this elution-treatedsolution is measured to obtain a value which is used as a standard ofwater-solubility. The lower the value of the electric conductivity, thebetter the water resisting property. And when this value issubstantially at most 200 μS/cm, the water resisting property is betterthan that of the glass compositions for bonding phosphors of the priorart, and when this value is at most 150 μS/cm, the water resistingproperty is further better. In the present invention, therefore, it isjudged that when the electric conductivity of the elution-treatedsolution of the glass composition, obtained in the above describedmanner, is at most 200 μS/cm, the water resisting property on practicaluse as a phosphor adhesive material can be maintained.

Example 1

CaO, B₂ O₃, Al₂ O₃ and Ta₂ O₅ shown as raw materials in Table 1 wereadequately mixed in a proportion of 20:60:15:5 by mole, charged in aplatinum crucible, heated and melted in an electric furnace at 1400° C.for 120 minutes, quenched and crushed in a mortar, thus obtaining aglass composition of Example 1.

The softening point and water-solubility of the glass composition inExample 1 were measured to obtain results shown in Table 1. Thesoftening point was 670° C. and the water-solubility was 40 μS/cm, bothsatisfying the requisite as the adhesive material for forming afluorescent film of a fluorescent lamp.

Comparative Example 1

For comparison, a glass composition of Comparative Example 1 wasprepared in an analogous manner to the glass composition of Example 1except mixing CaO, B₂ O₃ and Al₂ O₃ shown as raw materials in Table 2 ina proportion of 25:50:25 by mole.

When the softening point and water-solubility of the glass compositionin Comparative Example 1 were measured by the above described method,the softening point was 665° C. as shown in Table 2, which was in thescope of the target softening point of 600° to 700° C., but thewater-solubility was 423 μS/cm, which was larger than the aimed level,200 μS/cm. Namely, the water resisting property was not sufficient.

Examples 2 to 39 and Comparative Examples 2 to 15

Glass compositions of Examples 2 to 39 and Comparative Examples 2 to 15were prepared in an analogous manner to the glass compositions ofExample 1 and Comparative Example 1, except mixing the raw materials inproportions shown in Tables 1 and 2 by mole and the softening points andwater-solubilities of these glass compositions were measured by theabove described method, thus obtaining results shown in Tables 1 and 2.

                                      TABLE 1                                     __________________________________________________________________________    Glass Composition Compounding Ratio                                                                        Softening                                                                          Water                                       xMO      yB.sub.2 O.sub.3                                                                   zM'.sub.2 O.sub.3                                                                  uM"O.sub.2                                                                         vM"'.sub.2 O.sub.5                                                                 Point                                                                              Solubility                                  Example                                                                            M x B.sub.2 O.sub.3                                                                  y M'                                                                              z  M"                                                                              u  M"'                                                                              v (°C.)                                                                       (μS/cm)                                  __________________________________________________________________________    1    Ca                                                                              20                                                                              B.sub.2 O.sub.3                                                                  60                                                                              Al                                                                              15 --                                                                              -- Ta 5 670  40                                          2    Zn                                                                              55                                                                              B.sub.2 O.sub.3                                                                  40                                                                              --                                                                              -- Zr                                                                              5  -- --                                                                              603  6                                           3    Ca                                                                              25                                                                              B.sub.2 O.sub.3                                                                  50                                                                              Al                                                                              24.5                                                                             --                                                                              -- Ta 0.5                                                                             666  198                                         4    Ca                                                                              25                                                                              B.sub.2 O.sub.3                                                                  50                                                                              Al                                                                              24 --                                                                              -- Ta 1 666  184                                         5    Ca                                                                              25                                                                              B.sub.2 O.sub.3                                                                  50                                                                              Al                                                                              22 --                                                                              -- Ta 3 668  163                                         6    Ca                                                                              25                                                                              B.sub.2 O.sub.3                                                                  50                                                                              Al                                                                              15 --                                                                              -- Ta 10                                                                              683  14                                          7    Ca                                                                              25                                                                              B.sub.2 O.sub.3                                                                  50                                                                              Al                                                                              5  --                                                                              -- Ta 20                                                                              694  7                                           8    Ca                                                                              25                                                                              B.sub.2 O.sub.3                                                                  50                                                                              Al                                                                              20 --                                                                              -- Nb 5 648  80                                          9    Ca                                                                              25                                                                              B.sub.2 O.sub.3                                                                  50                                                                              Sc                                                                              20 --                                                                              -- Ta 5 675  158                                         10   Ca                                                                              15                                                                              B.sub.2 O.sub.3                                                                  70                                                                              Y 10 --                                                                              -- Ta 5 680  183                                         11   Ca                                                                              15                                                                              B.sub.2 O.sub.3                                                                  70                                                                              Eu                                                                              10 --                                                                              -- Ta 5 674  176                                         12   Mg                                                                              25                                                                              B.sub.2 O.sub.3                                                                  50                                                                              Al                                                                              20 --                                                                              -- Ta 5 692  25                                          13   Ca                                                                              25                                                                              B.sub.2 O.sub.3                                                                  50                                                                              Al                                                                              20 --                                                                              -- Ta 5 672  72                                          14   Sr                                                                              25                                                                              B.sub.2 O.sub.3                                                                  50                                                                              Al                                                                              20 --                                                                              -- Ta 5 634  98                                          15   Ba                                                                              25                                                                              B.sub.2 O.sub.3                                                                  50                                                                              Al                                                                              20 --                                                                              -- Ta 5 614  142                                         16   Ca                                                                              25                                                                              B.sub.2 O.sub.3                                                                  50                                                                              Al                                                                              15 Ti                                                                              5  Nb 5 665  42                                          17   Ca                                                                              25                                                                              B.sub.2 O.sub.3                                                                  50                                                                              Al                                                                              15 Zr                                                                              5  Nb 5 672  35                                          18   Ca                                                                              25                                                                              B.sub.2 O.sub.3                                                                  50                                                                              Al                                                                              15 Th                                                                              5  Nb 5 665  19                                          19   Zn                                                                              40                                                                              B.sub.2 O.sub.3                                                                  50                                                                              Al                                                                              10 --                                                                              -- -- --                                                                              646  11                                          20   Zn                                                                              20                                                                              B.sub.2 O.sub.3                                                                  50                                                                              Al                                                                              30 --                                                                              -- -- --                                                                              685  35                                          21   Zn                                                                              60                                                                              B.sub.2 O.sub.3                                                                  30                                                                              --                                                                              -- Si                                                                              10 -- --                                                                              651  58                                          22   Zn                                                                              30                                                                              B.sub.2 O.sub.3                                                                  50                                                                              --                                                                              -- Th                                                                              20 -- --                                                                              696  12                                          23   Zn                                                                              40                                                                              B.sub.2 O.sub.3                                                                  50                                                                              Sc                                                                              5  Ti                                                                              5  -- --                                                                              657  33                                          24   Zn                                                                              40                                                                              B.sub.2 O.sub.3                                                                  50                                                                              Al                                                                              5  Hf                                                                              5  -- --                                                                              660  42                                          25   Zn                                                                              30                                                                              B.sub.2 O.sub.3                                                                  60                                                                              --                                                                              -- --                                                                              -- Ta 10                                                                              676  8                                           26   Zn                                                                              20                                                                              B.sub.2 O.sub.3                                                                  65                                                                              --                                                                              -- --                                                                              -- Nb 15                                                                              694  15                                          27   Zn                                                                              50                                                                              B.sub.2 O.sub.3                                                                  50                                                                              --                                                                              -- --                                                                              -- -- --                                                                              626  89                                          28   Zn                                                                              25                                                                              B.sub.2 O.sub.3                                                                  50                                                                              Al                                                                              20 --                                                                              -- Ta 5 680  8                                           29   Ca                                                                              25                                                                              B.sub.2 O.sub.3                                                                  50                                                                              Sc                                                                              15 Ti                                                                              5  Nb 5 665  42                                          30   Ca                                                                              25                                                                              B.sub.2 O.sub.3                                                                  50                                                                              Sc                                                                              15 Zr                                                                              5  Nb 5 665  35                                          31   Ca                                                                              25                                                                              B.sub.2 O.sub.3                                                                  50                                                                              Sc                                                                              15 Th                                                                              5  Nb 5 665  19                                          32   Zn                                                                              48                                                                              B.sub.2 O.sub.3                                                                  40                                                                              Al                                                                              12 --                                                                              -- -- --                                                                              611  6                                           33   Zn                                                                              32                                                                              B.sub.2 O.sub.3                                                                  60                                                                              Al                                                                              8  --                                                                              -- -- --                                                                              652  9                                           34   Zn                                                                              30                                                                              B.sub.2 O.sub.3                                                                  40                                                                              Al                                                                              30 --                                                                              -- -- --                                                                              667  12                                          35   Zn                                                                              25                                                                              B.sub.2 O.sub.3                                                                  50                                                                              Al                                                                              25 --                                                                              -- -- --                                                                              670  16                                          36   Zn                                                                              20                                                                              B.sub.2 O.sub.3                                                                  60                                                                              Al                                                                              20 --                                                                              -- -- --                                                                              675  25                                          37   Zn                                                                              60                                                                              B.sub.2 O.sub.3                                                                  40                                                                              --                                                                              -- --                                                                              -- -- --                                                                              605  45                                          38   Zn                                                                              58                                                                              B.sub.2 O.sub.3                                                                  37                                                                              Al                                                                              5  --                                                                              -- -- --                                                                              615  22                                          39   Zn                                                                               5                                                                              B.sub.2 O.sub.3                                                                  68                                                                              Al                                                                              27 --                                                                              -- -- --                                                                              682  128                                         __________________________________________________________________________

                                      TABLE 2                                     __________________________________________________________________________    Compara-                                                                           Glass Composition Compounding Ratio                                                                   Softening                                                                          Water                                       tive xMO yB.sub.2 O.sub.3                                                                   zM'.sub.2 O.sub.3                                                                  uM"O.sub.2                                                                         vM"'.sub.2 O.sub.5                                                                 Point                                                                              Solubility                                  Example                                                                            M x B.sub.2 O.sub.3                                                                  y M'                                                                              z  M"                                                                              u  M"'                                                                              v (°C.)                                                                       (μS/cm)                                  __________________________________________________________________________    1    Ca                                                                              25                                                                              B.sub.2 O.sub.3                                                                  50                                                                              Al                                                                              25 --                                                                              -- -- --                                                                              665  423                                         2    Mg                                                                              40                                                                              B.sub.2 O.sub.3                                                                  50                                                                              Al                                                                              10 --                                                                              -- -- --                                                                              700  413                                         3    Ca                                                                              40                                                                              B.sub.2 O.sub.3                                                                  50                                                                              Al                                                                              10 --                                                                              -- -- --                                                                              672  685                                         4    Ba                                                                              40                                                                              B.sub.2 O.sub.3                                                                  50                                                                              Al                                                                              10 --                                                                              -- -- --                                                                              618  1050                                        5    Ca                                                                              40                                                                              B.sub.2 O.sub.3                                                                  50                                                                              Al                                                                              10 --                                                                              -- -- --                                                                              700  800                                         6    Ca                                                                              30                                                                              B.sub.2 O.sub.3                                                                  50                                                                              Al                                                                              20 --                                                                              -- -- --                                                                              670  600                                         7    Ca                                                                              20                                                                              B.sub.2 O.sub.3                                                                  50                                                                              Al                                                                              30 --                                                                              -- -- --                                                                              670  520                                         8    Ca                                                                              25                                                                              B.sub.2 O.sub.3                                                                  50                                                                              Al                                                                              24.5                                                                             --                                                                              -- -- --                                                                              658  275                                                       La                                                                              0.5                                                           9    Ca                                                                              25                                                                              B.sub.2 O.sub.3                                                                  50                                                                              Al                                                                              24 --                                                                              -- -- --                                                                              655  253                                                       La                                                                              1                                                             10   Ca                                                                              25                                                                              B.sub.2 O.sub.3                                                                  50                                                                              Al                                                                              22 --                                                                              -- -- --                                                                              652  212                                                       La                                                                              3                                                             11   Zn                                                                              16                                                                              B.sub.2 O.sub.3                                                                  80                                                                              Al                                                                              4  --                                                                              -- -- --                                                                              Devitrification                                  12   Zn                                                                              64                                                                              B.sub.2 O.sub.3                                                                  20                                                                              Al                                                                              16 --                                                                              -- -- --                                                                              Devitrification                                  13   Zn                                                                              15                                                                              B.sub.2 O.sub.3                                                                  40                                                                              Al                                                                              45 --                                                                              -- -- --                                                                              Devitrification                                  14   Zn                                                                              75                                                                              B.sub.2 O.sub.3                                                                  25                                                                              Al                                                                              0  --                                                                              -- -- --                                                                              Devitrification                                  15   Zn                                                                               3                                                                              B.sub.2 O.sub.3                                                                  75                                                                              Al                                                                              22 --                                                                              -- -- --                                                                              Devitrification                                  __________________________________________________________________________

DISCUSSION

It is evident from Examples 3 to 7 that when the quantity of Al₂ O₃ isdecreased and that of Ta₂ O₅ is increased, there is provided an effectthat the water-solubility of the resulting glass composition isdecreased.

As apparent from comparison of Examples 8 and 9, there is obtained aglass composition having a lower water-solubility in the case of usingAl₂ O₃ as M'₂ O₃ rather than Sc₂ O₃.

As apparent Examples 16 to 18, there are obtained a glass compositionhaving a lower water-solubility in the case of using ZrO₂ as atetra-valent metal oxide (M"O₂) than TiO₂ and a glass composition havingthe lowest water-solubility, i.e. best water resisting property in thecase of using ThO₂.

As apparent from comparison of Example 19 and Comparative Examples 2 to4, the water-solubility of a glass composition in the case of using ZnOas a divalent metal oxide (MO) is much smaller than in the case of usingother divalent metal oxides than ZnO, teaching that the water resistingproperty is markedly improved in the former case.

As apparent from Examples 19 to 20, in the case of using ZnO as adivalent metal oxide (MO), there is a tendency such that the watersolubility of the resulting glass composition is increased and thewater-resisting property is lowered with decrease of the content of ZnO.

In these Examples, the glass compositions obtained using, as MO, ZnO ina quantity of 20 to 60 mol % are particularly excellent in waterresisting property.

Examples 40 to 78

A phosphor was suspended in water with polyethylene oxide (binder) and 3weight % based on the phosphor of each of the glass compositions(adhesive material) of Examples 1 to 39, adequately crushed, andadequately mixed to prepare a phosphor-coating liquid. Thisphosphor-coating liquid was applied to a glass tube, subjected to bakingat 500° C. for 8 minutes and a linear fluorescent lamp of 40 W wasprepared in an ordinary manner. The resulting fluorescent lamps allshowed a white body color and even when Ar was rapidly introduced fromvacuum in an evacuating step, there was found no peeling of thefluorescent film at the tube end.

Comparative Examples 16 to 30

When Example 40 was repeated except using each of the glass compositionsof Comparative Examples 1 to 15 as an adhesive material to prepare afluorescent lamp, the resulting fluorescent lamps each showed a blackishbody color and lowered emission efficiency.

Example 79

When Example 40 was repeated except using 0.5 weight %, 1 weight %, 2weight %, 5 weight % and 8 weight % of the glass composition powder ofExample 2 as an adhesive material to prepare a fluorescent lamp, theresulting fluorescent lamps each showed white body color and even whenAr was rapidly introduced from vacuum in an evacuating step, there wasfound no peeling of the fluorescent film at the tube end.

Comparative Example 31

When Example 40 was repeated except using 0.02 weight % of the glasscomposition powder of Example 2 as an adhesive material to prepare afluorescent lamp, the resulting fluorescent lamp showed peeling of thefluorescent film when Ar was rapidly introduced from vacuum in anevacuating step.

Comparative Example 32

When Example 40 was repeated except using 15 weight % of the glasscomposition powder of Example 2 as an adhesive material to prepare afluorescent lamp, the resulting fluorescent lamp showed no peeling ofthe fluorescent film even when Ar was rapidly introduced from vacuum inan evacuating step, but the packed state of the phosphor grains coatedonto the tube wall was so bad that there was obtained asurface-roughened coating film and the emission efficiency was lowered.

UTILITY AND POSSIBILITY ON COMMERCIAL SCALE

According to the construction element of the present invention, therecan be provided a low melting point glass, which has a good softeningpoint as well as high water resisting property and which is excellent asan adhesive material and in particular, suitable for bonding a glasstube and a fluorescent film, in the production of a fluorescent lamp.

We claim:
 1. A fluorescent lamp, in which a glass composition forbonding a phosphor, represented by the general formula,

    xMO.yB.sub.2 O.sub.3.zM'.sub.2 O.sub.3.uM"O.sub.2.vM'".sub.2 O.sub.5

wherein M is at least one element selected from the group consisting ofMg, Ca, Sr, Ba and Zn, M' is at least one element selected from thegroup consisting of Al, Sc, Y and lanthanoid elements, M" is at leastone element selected from the group consisting of Ti, Zr, Hf, Th and Si,M'" is a least one element selected from the group consisting of Nb andTa, x, y, z, u and v satisfy the relationships of 0<x≦70, 15≦y≦80,0≦z≦50, 0≦u≦30, 0≦v≦30, 0.5≦u+v≦50 and x+y+z+u+v=100, represented by mol%, is incorporated in a phosphor layer on the inner surface of a glasstube.
 2. The fluorescent lamp as claimed in claim 1, wherein x, y, z, uand v satisfy the relationships of 5≦x≦65, 30≦y≦70, 0≦z≦40, 0≦u≦30,0≦v≦20 and 1≦u+v≦40, represented by mol %.
 3. A fluorescent lamp, inwhich a glass composition for bonding a phosphor, represented by thegeneral formula,

    xZnO.yB.sub.2 O.sub.3.zM'.sub.2 O.sub.3.vM"O.sub.2.vM'".sub.2 O.sub.5

wherein M' is at least one element selected from the group consisting ofAl and Sc, M" is at least one element selected from the group consistingof Ti, Zr, Hf, Th and Si, M'" is at least one element selected from thegroup consisting of Nb and Ta, x, y, z, u and v satisfy therelationships of 5≦x≦70, 25≦y≦75, 0≦z≦40, 0≦u≦30, 0≦v≦30 andx+y+z+u+v=100, represented by mol %, is incorporated in a phosphor layeron the inner surface of a glass tube.
 4. The fluorescent lamp as claimedin claim 3, wherein x, y, z, u and v satisfy the relationships of10≦x≦65, 30≦y≦65, 0≦z≦35, 0≦u≦25 and 0≦v≦20, represented by mol %. 5.The fluorescent lamp as claimed in claim 1 or 3, wherein the glasscomposition has a softening point in a temperature range of 600° to 700°C.
 6. The fluorescent lamp as claimed in claim 1 or 3, wherein the glasscomposition has a water solubility of at most 200 μS/cm represented byelectric conductivity.
 7. The fluorescent lamp as claimed in claim 1 or3, wherein the glass composition is incorporated in the phosphor layeron the inner surface of the glass tube in a proportion of 0.1 to 10weight % based on the phosphor.